1. Field of the Invention
The present invention relates to a semiconductor device and a method for fabricating the same. More particularly, it relates to a semiconductor device in which a thin film transistor is formed using a metal induced crystallization (MIC) method and a metal induced lateral crystallization (MILC) method and a capacitor is formed using the MIC method.
2. Discussion of the Background
Flat panel display devices such as liquid crystal display devices, organic electro-luminescence display devices and plasma display panels have drawn recent attention as replacement displays for the larger and heavier cathode ray tube.
In a flat panel display device such as the organic electro-luminescence display device and the liquid crystal display device, a thin film transistor may be used as a switching device and a driving device, and a capacitor may be coupled with the thin film transistor to store external signals and supply the stored signals in a following signal period.
FIG. 1A, FIG. 1B and FIG. 1C are cross-sectional views showing a conventional method for forming a thin film transistor and a capacitor.
First, FIG. 1A is a cross-sectional view for showing a process of forming a semiconductor layer of a thin film transistor and a first electrode of a capacitor on an insulating substrate. As FIG. 1A shows, a buffer layer 12 may be formed on a transparent insulating substrate 11, which may be made of plastic or glass. An amorphous silicon layer may then be formed on the buffer layer 12 and patterned to form a semiconductor layer 13 of the thin film transistor and the first electrode 14 of the capacitor.
A first insulation layer 15, which simultaneously serves as a gate insulator of the thin film transistor and an insulation layer of the capacitor, may be formed on the substrate. The first insulation layer 15 may be a silicon oxide or silicon nitride layer.
FIG. 1B is a cross-sectional view for showing a process of crystallizing the patterned amorphous silicon layer and forming a gate electrode of the thin film transistor and a second electrode of the capacitor. As FIG. 1B shows, polycrystalline silicon layers 13a, 14a may be formed by crystallizing the amorphous silicon semiconductor layer 13 and the first electrode 14. Although there are various crystallization methods, a common crystallization method includes charging the substrate into a furnace and performing crystallization at a certain temperature for a long time.
After forming the polycrystalline silicon layers 13a, 14a, a conductor may be formed on the substrate and patterned, thereby forming a gate electrode 16 of the thin film transistor and a second electrode 17 of the capacitor, thereby completing the capacitor comprising the first electrode 14a, the insulation layer 15 and a second electrode 17.
FIG. 1C is a cross-sectional view for showing a process of forming a second insulation layer on the substrate and forming source/drain electrodes on the second insulation layer. As FIG. 1C shows, a second insulation layer 18, which serves as an interlayer dielectric of the thin film transistor, may be formed on the substrate.
Contact holes that expose portions of source/drain regions of the semiconductor layer 13a may then be formed in the first insulation layer 15 and the second insulation layer 18. Next, forming source/drain electrodes 19 on the contact holes completes the thin film transistor.
Therefore, the thin film transistor's semiconductor layer, gate insulator and gate electrode may be simultaneously formed with the capacitor's first electrode, insulation layer and second electrode, respectively, and the semiconductor layer and the first electrode may be crystallized by the same crystallization method.
However, a method for forming a semiconductor device such as the thin film transistor and the capacitor may require lengthy heat treatment since the capacitor's first electrode may be much larger than the thin film transistor's channel region, and the lengthy heat treatment process may shrink or warp the substrate. Additionally, capacitance may decrease since the capacitor's insulation layer is simultaneously formed with the gate insulator, which may be thicker than necessary for the capacitor.